Epistates/TurboMCP

[3.0.8] - 2026-03-24

Added

• Multi-version MCP protocol support — TurboMCP can now negotiate and serve multiple MCP specification versions from a single server. The version adapter system transparently filters outgoing responses to match the client's negotiated protocol version.

• ProtocolVersion enum — Replaced type ProtocolVersion = String alias with a proper enum (V2025_06_18, V2025_11_25, Draft, Unknown(String)). Provides Serialize/Deserialize (round-trips to canonical version strings), Ord (by release date), Display, From<&str>, From<String>, PartialEq<&str>, is_stable(), is_known(), and is_draft(). Constants: ProtocolVersion::LATEST and ProtocolVersion::STABLE.

• Version adapter layer (turbomcp_protocol::versioning::adapter) — VersionAdapter trait with filter_capabilities(), filter_result(), validate_method(), and supported_methods(). Factory function adapter_for_version() returns the appropriate adapter. Three implementations:

  • V2025_06_18Adapter — strips icons, execution, outputSchema from tools; icons from prompts/resources; description/icons/websiteUrl from serverInfo; tasks capability; elicitation.url sub-capability; sampling.tools sub-capability. Rejects tasks/* methods.
  • V2025_11_25Adapter — pass-through (current stable).
  • DraftAdapter — pass-through (superset of 2025-11-25).

• route_request_versioned() — New server router entry point for post-initialize requests. Validates incoming methods against the negotiated version and filters outgoing responses through the version adapter. Transport layers store the negotiated version from init and call this for subsequent requests.

• ProtocolConfig::multi_version() — Opt-in constructor that accepts all stable MCP versions. The default remains strict latest-only (matching prior behavior).

• ElicitationCapabilities spec compliance — Added form and url sub-capability structs per MCP 2025-11-25 specification. Empty capabilities object ({}) defaults to form-only support via supports_form()/supports_url() helpers. Builder defaults to full (form + URL). schema_validation retained as TurboMCP extension.

• 39 new version adapter tests — Comprehensive coverage: serde round-trips, ordering consistency, adapter filtering for every response type, method validation, elicitation backward compat, end-to-end initialize response filtering.

Fixed

• Ord/PartialEq inconsistency on ProtocolVersion::Unknown — Two distinct Unknown variants were Ord::Equal but PartialEq not-equal, violating Rust's trait contract and causing undefined behavior in BTreeMap/BTreeSet/sort. Unknown variants now compare lexicographically by inner string.

• ElicitationCapabilities missing form/url sub-fields — The 2025-11-25 spec requires { "form": {}, "url": {} } structure in elicitation capabilities. Previously only had schema_validation.

Changed

• SUPPORTED_VERSIONS expanded — Now includes both "2025-06-18" and "2025-11-25" (previously only "2025-11-25"). The default ProtocolConfig still only accepts the latest version; use ProtocolConfig::multi_version() to accept older clients.

• ProtocolConfig uses ProtocolVersion enum — preferred_version and supported_versions fields are now typed ProtocolVersion instead of String. negotiate() returns Option<ProtocolVersion>.

Full Changelog: https://github.com/Epistates/turbomcp/compare/v3.0.7...v3.0.8